[ Python 常見問題 ] Python dynamic instantiation from string name of a class

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Question 
In python, I have to instantiate certain class, knowing its name in a string, but this class 'lives' in a dynamically imported module. An example follows: 
loader-class script: 

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1. import sys  
2. class loader:  
3.   def __init__(self, module_name, class_name): # both args are strings  
4.     try:  
5.       __import__(module_name)  
6.       modul = sys.modules[module_name]  
7.       instance = modul.class_name() # obviously this doesn't works, here is my main problem!  
8.     except ImportError:  
9.        # manage import error  

Some-dynamically-loaded-module script: 

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1. class myName:  
2.   # etc...  

I use this arrangement to make any dynamically-loaded-module to be used by the loader-class following certain predefined behaviours in the dyn-loaded-modules... 

How-To 
You can use getattr 

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1. getattr(module, class_name)  

to access the class. More complete code: 

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1. module = __import__(module_name)  
2. class_ = getattr(module, class_name)  
3. instance = class_()  

A simple example as below. Consider you have test.py in current path: 

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1. class Hello:  
2.     def __init__(self, name):  
3.         self.name = name  
4.   
5.     def hello(self):  
6.         print("Hello {}".format(self.name))  

Then you can initialize the Hello class this way: 

>>> test_module = __import__('test') 
>>> helloClass = getattr(test_module, 'Hello') 
>>> helloObj = helloClass('John') 
>>> helloObj.hello() 
Hello John